The present application relates to an anti-glare film, a method for manufacturing the same, and a display device using the same. Specifically, the present application relates to an anti-glare film used for the surface of a display device, such as a liquid crystal display, a plasma display, an electroluminescence display, or a cathode ray tube (CRT) display, a method for manufacturing the same, and a display device using the same.
In display devices, such as a liquid crystal display, a plasma display, and a CRT display, when ambient light from fluorescent lighting or the like is reflected in the surface of a display device, the visibility becomes markedly poor. Therefore, there has been employed a method in which an optical multilayer film or a low refractive-index film is formed on the surface of a display device to reduce the reflectance of the surface or a method in which an anti-glare film having a finely uneven surface is formed on the surface of a display device to cause diffuse reflection of ambient light so that the reflected images are blurred.
However, the use of an optical multilayer film increases the production cost, and does not achieve satisfactory anti-glare properties. When the increase of the production cost is suppressed by using a low refractive-index film, the resultant surface has a relatively high reflectance, and hence a problem of annoying reflection in the surface arises. On the other hand, in the method in which a mixture of silica filler, organic filler or the like is incorporated to form a surface having fine irregularities and a reflection in the surface of a display is blurred utilizing diffuse reflection, anti-glare properties can be obtained; however, the appearance of white muddiness is strong, and especially when ambient light is strong, the contrast is reduced, so that the visibility becomes poor.
In recent years, a surface treatment which suppresses the appearance of white muddiness and increases the contrast while suppressing appearance of white muddiness is desired, and some methods for the treatment have been developed. For example, in the Japanese Unexamined Patent Application Publication No. 2002-365410 (hereinafter referred to as “Patent Document 1”), a method for obtaining an anti-glare film unlikely to be whitish while preventing reflection in the surface is disclosed wherein, the ratio of an intensity of a reflected light deviated at 20° with respect to the specular reflection direction to a specular reflection intensity of an incident light upon the direction at −10° with respect the normal to the surface of the anti-glare film is 0.2 or less and the half band width of a peak of the reflected light intensity is 7° or more.
In the Japanese Unexamined Patent Application Publication No. 2004-61853 (hereinafter referred to as “Patent Document 2”) discloses an anti-glare film in which the specular reflectance of the incident light collimated at an angle of 5° with the normal to the surface of the anti-glare film is substantially equal to the reflectance toward the specular reflection direction of the incident light at an angle deviated by 0.2° from the specular reflection. In addition, the Patent Document 2 also discloses a method for obtaining an anti-glare film having a value of 1/1,000 or less in which the value is obtained by normalizing the reflected light intensity toward the normal direction with respect to the incident light upon the anti-glare film at 20° or more using a standard diffuser plate in the same measurement (hereinafter, the reflected light intensity normalized using an intensity of the reflected light from a standard diffuser plate is referred to as “gain”).
The Japanese Unexamined Patent Application Publications No. 2006-53371 and No. 2004-240411 (hereinafter referred to as “Patent Document 3” and “Patent Document 4”, respectively) have descriptions of a method for obtaining an anti-glare film in which, the regular reflectance is 1% or less with respect to the incident light upon the anti-glare film at an angle of incidence of 5° to 30°, and the ratio of the reflectance toward 30° or more with respect to the specular reflection direction to the specular reflectance is 0.001 or less.
However, there is a trade-off between anti-glare properties and suppression of the appearance of white muddiness, and it is difficult to design an anti-glare film having both the properties, and the solution has been not good enough. For example, it has been found that a known anti-glare film having surface irregularities formed using silica filler satisfies the diffuse reflection characteristics specified in the patent document 1 and the anti-glare film exhibits a strong appearance of white muddiness although the intensity ratio is 0.1 or less, and the anti-glare film can achieve anti-glare properties while the half band width is 7° or less.
The diffuse reflection characteristics described in the patent document 2, in which the specular reflectance is substantially equal to the reflectance toward the specular direction of the incident light deviated from an angle by 0.2° to the specular reflection, are satisfied by a film having a surface state close to the mirror reflection, and therefore it is difficult to obtain anti-glare properties merely by the technique described in the Patent Document 2. On the other hand, from the studies made by the present inventors, it has been found that, even when the gain to the normal direction is about 1/100, the appearance of white muddiness of the film can be satisfactorily lowered although it is difficult to actually prepare an anti-glare film having characteristics such that the gain to the normal direction is 1/1,000 or less.
Regarding the diffuse reflection characteristics specified in the Patent Documents 3 and 4, it has been found that there are cases where an anti-glare film achieves a regular reflectance of 1% or less even though the anti-glare film has a relatively even surface and a large reflection. In addition, it has been found that an anti-glare film subjected to a low-reflection treatment, for example, a low refractive index layer formed on the surface, satisfies such diffuse reflection characteristics, but the anti-glare properties are not good enough.
Further, as described above, an anti-glare film having fine irregularities in the surface provides anti-glare properties, but it has a problem in that the film has a rough surface appearance on visual perception. When an anti-glare film having a large rough surface appearance is used in a display device, the viewability of an image becomes lowered.